Internal bleeding is a significant cause of death in cases of trauma, and rapid and effective diagnosis of patients with uncontrolled bleeding has long been recognized as an important goal to lower mortality and morbidity. Currently, internal bleeding is diagnosed using angiography, Computed Tomography (CT), diagnostic peritoneal lavage, B-mode ultrasound, and exploratory laparotomy, while surgical intervention is the most common treatment option. The detection of a bleeding site (i.e., diagnostic imaging) and the closure of a bleeding wound should preferably be accomplished as quickly as possible to minimize blood loss in a patient and reduce mortality and morbidity associated with such blood loss.
Advances in duplex and color-flow ultrasound in the last two decades have had a significant clinical impact on vascular diagnosis. For example, the use of Doppler ultrasound has been shown to be effective for targeting a bleeding site, as disclosed in a paper by R. W. Martin, S. Vaezy, P. Kaczkowski, G. Keilman, S. Carter, M. Caps, K. W. Beach, M. I. Plett, and L. A. Crum, entitled “Hemostasis of punctured vessels using Doppler-guided high-intensity ultrasound,” Ultrasound Med. Biol., vol. 25, pp. 985-990, 1999. However, this technique suffers from the disadvantage of imaging a limited region of interest. Although color-flow ultrasound can image a large region of interest, currently it lacks sufficient sensitivity for diagnosing internal bleeding, due to weak scattering from blood and the slow flow velocity of blood bleeding from a wound, especially in the case of deep bleeds and organ bleeds. In a paper by X. Shi, R. W. Martin, S. Vaezy, and L. A. Crum, entitled “Quantitative investigation of acoustic streaming in blood,” J. Acoust. Soc. Am., vol. 111, pp. 1110-1121, 2002, the use of acoustic streaming is proposed for distinguishing between stagnant blood and tissue using color-flow images. However this paper does not suggest how to detect a bleeding site with acoustic streaming. The use of contrast agents has also shown to be promising for localizing active bleeding sites, as discussed in a paper by J-B Liu, D. A. Merton, B. B. Goldberg, N. M. Rawool, W. T. Shi, and F. Forsberg, entitled “Contrast-enhanced two- and three-dimensional sonography for revaluation of intra-abdominal hemorrhage,” J. Ultrasound Med, vol. 21, pp. 161-169, 2002. Yet, the use of contrast agents is time-consuming and can sometimes be dangerous.
Each of these prior art techniques for detecting bleeding is unable to provide efficient real-time images in which the location of a bleeding site can be rapidly identified. Also, as discussed in greater detail below, simply using conventional color-flow data for imaging a site cannot readily distinguish between pooled blood and bleeding at the site. Accordingly, it is necessary to develop a new method for rapid diagnosis of internal bleeding.
Physical examination is an important element of the initial assessment of a trauma patient with suspected internal bleeding. If an audible “bruit” or a palpable “thrill” is found upon physical examination, further diagnostic tests for internal bleeding or surgical intervention are often recommended. It has now been established that bruits and thrills are produced by the forces exerted on vessel walls by eddies created as blood flows from a high-pressure region to a low-pressure region through a narrow orifice. The pressure fluctuations in eddies cause local vibrations in the vessel wall and surrounding tissue and manifest either as bruits or thrills at the skin surface. The power spectrum of the vibrations exhibits a frequency peak called the “break frequency,” which is directly related to the diameter of the orifice and the local flow velocity through the Strouhal number. In conventional color-flow ultrasound images, tissue vibrations from abnormal blood flow produce characteristic speckled artifacts in the surrounding tissue. But, these artifacts are difficult to interpret and are not quantitative. Tissue vibrations have been previously studied using one-dimensional (1D) pulsed Doppler ultrasound, and the prior art includes disclosure of a wavelet-based method for detecting and characterizing arterial vibrations in internal bleeding (M. I. Plett, “Ultrasonic arterial vibrometry with wavelet-based detection and estimation,” PhD. dissertation, Univ. of Washington, 2000). However, this pulsed Doppler-based technique also has a limited field of view, and is along a single scan line. Furthermore, as disclosed in this paper, the processing was done off-line, so it was not possible to create images interactively in real time.
Accordingly, it would be desirable to develop a new tissue vibration detection and imaging mode for ultrasound instruments in which vibrations produced by blood flow eddies can be detected and color-coded according to their amplitude and frequency and overlaid on a B-mode and/or a color-flow image in real time. The tissue vibration imaging mode might then be used for locating the origin of the vibration more precisely, relative to the patient's anatomy and/or for obtaining simultaneous information about vibrations and the underlying blood flow. Acoustic hemostasis using High Intensity Focused Ultrasound (HIFU) is a promising new technique for stopping internal bleeding without invasive surgical intervention. For effective targeting and monitoring of hemostasis, non-invasive real-time localization of a bleeding site in real time is essential. This new technique might thus be used both for diagnostic determination of a bleeding site, and optionally, in conjunction with HIFU or other desired therapy, for localizing the bleeding site in real time, so that therapy might be effectively applied to stop the bleeding as indicated in the U.S. Pat. No. 6,083,159, “Methods and devices for providing acoustic hemostasis”, U.S. Pat. No. 5,993,389, “Devices for providing acoustic hemostasis”, and U.S. Pat. No. 5,882,302, “Methods and devices for providing acoustic hemostasis”.